The chemical structure of a polysaccharide named Fucogel was characterized and the position of acetylation was identified by NMR. A conformational analysis was performed on this 3-sugar repeating unit. From this, the persistence length, characterizing the stiffness of the polysaccharide, was determined and the role of the presence of acetyl group, reducing the stiffness, was pointed out. The helical conformations were also predicted, one of these being in agreement with X-ray data obtained on a similar polysaccharide. Experimental characterization of the native and deacetylated polysaccharides was developed. SEC experiments allowed us to determine the molar mass and the persistence length on the deacetylated polysaccharide. The value is in good agreement with that predicted from the molecular modeling. Microcalorimetry, theology, and fluorescence spectroscopy demonstrated respectively that no helical conformation exists in solution but that loose interchain interactions due to the acetyl substituents exist in dilute solutions.